Question

A ⊆ B

S (B\A)=28, S(B)=5.S(A). S(A)=?

Answer 1

S(A) = 7

Explanation:

A ⊆B means A is a proper subset of B. That means all elements of set A are also elements of set B

S(B\A) means the set of all elements of B that are not in set A. This is given as 28

We are also given S(B) = 5.S(A)

Since A is a subset of B, S(B) = set of all elements in A and set of all elements in B but not in A

In other words
S(B) = S(A) + S(B\A)

Since S(B) = 5S(A) we get

5S(A) = S(A) + S(B\A)

5S(A) = S(A) + 28

5S(A) - S(A) = 28

4S(A) = 28

S(A) = 7